In view of an increasing shortage of petroleum deposits, the economic exploitation of raw materials containing organic constituents, such as oil or tar sands and oil shale, has become of greater interest. Oil or tar sands are mixtures of clay, sand, water and hydrocarbons. The latter can have different compositions and range from bitumen to normal crude oil. The hydrocarbon content in the sands is between about 1 and 18%. The economic efficiency of exploitation increases with the hydrocarbon content. Oil or tar sands can be recovered by surface mining. When extracting them from deeper soil layers, an initial processing of the oil or tar sand is already effected in situ. Steam is introduced into the deposit in order to liquefy the hydrocarbons. This kind of oil recovery therefore requires a great deal of water, which cannot be discharged entirely free from oil.
Oil shales are rocks which contain bitumen or low-volatility oils. The content of organic matter (kerogen) lies between about 10 and 30%. Oil shales are not shales in a petrographic sense, but layered, not schistous, sedimentary rocks. The recovery of hydrocarbons, such as oil from oil shale, is traditionally effected by mining and subsequent pyrolysis (carbonization at 500° C.). Subsurface recovery (in situ) is alternatively used by pressing a steam-air mixture into the rock previously loosened by blasting and ignition of a flame front, which expels the hydrocarbons such as oil.
The previous recovery of hydrocarbons, such as crude oil from oil or tar sands or oil shale is thus is relatively cost-intensive. With rising oil prices, the recovery of hydrocarbons, such as crude oil, from oil or tar sands and oil shale becomes increasingly interesting in economic terms. A problem in the present recovery of hydrocarbons, such as crude oil, from oil or tar sands and oil shales is the necessary high consumption of water and the emission of waste waters containing residual oil.
U.S. Pat. No. 4,507,195 describes a process for coking contaminated oil shale or tar sand oil on solids distilled in retorts. The hydrocarbonaceous solids are mixed with a hot heat transfer material, in order to raise the temperature of the solids to a temperature suitable for the pyrolysis of the hydrocarbons. The mixture is maintained in a pyrolysis zone until a sufficient amount of hydrocarbon vapors are released. In the pyrolysis zone, a stripping gas is passed through the mixture in order to lower the dew point of the resulting hydrocarbon vapors and entrain the fine particles. A mixture of contaminated hydrocarbon vapors, stripping gas and entrained fine particles is thereby obtained from the pyrolysis zone. From the contaminated hydrocarbon vapors, a heavy fraction is separated and thermally cracked in a fluidized bed consisting of fine particles, whereby the impurities together with coke are deposited on the fine particles in the fluidized bed. The product oil vapors are withdrawn from the coking container. As heat transfer material, recirculated pyrolyzed oil shale or tar sand is used, which was guided through a combustion zone, in order to burn carbon residues and provide the heat for the pyrolysis of the raw material. Since there is no pressure seal between the combustion zone and the pyrolysis furnace, the oxidizing atmosphere of the combustion zone can enter the pyrolysis furnace and impair the quality of the oil vapor. Thermal cracking in the coking container also consumes a great deal of energy and is therefore expensive.
EP 1 015 527 B1 describes a process for the thermal treatment of feedstock containing volatile, combustible constituents, wherein the feedstock is mixed with hot granular solids from a collecting bin in a pyrolysis reactor, in which relatively high temperatures exist. This should lead to cracking reactions in the gases and vapors in the reactor.
Besides the thermal cracking used in the above-mentioned processes, catalytic cracking processes are known. In Fluid Catalytic Cracking (FCC), the heavy distillate of a refinery is decomposed to gases, liquefied gases and gasolines, for example to long-chain n-alkanes and i-alkanes. Cracking is generally effected at temperatures between 450 and 550° C. and a reactor pressure of 1.4 bar by means of an alumosilicate-based zeolite catalyst. FCC crackers are described for instance in U.S. Pat. No. 7,135,151 B1, US 2005/0118076 A1 or US 2006/0231459 A1. An exemplary catalyst is disclosed in WO 2006/131506 A1. Further possibilities for the further treatment of hydrocarbon fractions include hydrotreatment and hydrocracking.
In a refining plant for raw materials containing organic constituents, such as oil-containing raw materials, the latter, for example, oil sand, can first be supplied to drying, then to preheating, then to an expulsion stage, and finally the residual solids can be supplied to a combustion stage. Drying is effected at, for example, about 80 to 120° C., and preheating at, for example, about 150 to 300° C. The expulsion stage operates at, for example, about 300 to 1000° C. In all three stages, hydrocarbonaceous vapors (oil vapors) are released, which are supplied to a processing stage (for example, by hydrocracking, coking and/or hydrotreating) and are further processed there. The residual solids of the expulsion stage can be introduced into a combustion stage and be burnt at, for example, about 1000 to 1200° C. The solid combustion products can be utilized, for instance, to heat up the expulsion stage. In most cases, the individual stages (drying, preheating, expulsion and combustion) can be operated as fluidized beds. As fluidizing gas, light hydrocarbons, inert gas (such as nitrogen), oxygen-containing gases, CO2-containing gases or also waste gases of the combustion stage can be used. For the processing stage, hydrogen is also required beside the oil vapors (for example, for hydrocracking).
The qualities of oil-containing raw materials often are very different and fluctuating, so that in some cases only very little oil vapors are released in the expulsion stage or in a preceding stage, and that bitumen of the oil-containing raw materials tend to liquefy or coke instead of evaporating. The yield of desired oil vapors is reduced thereby and often more energy is produced in the combustion stage, which is not desired. The coking tendency of the oil increases with increasing temperature. In the case of higher-quality oil-containing raw materials, such as oil sands, which contain a great deal of oil and release their oil content simply, the relation between the generation of heat in the combustion stage and the generation of oil vapor in the expulsion stage can be accomplished by controlling the temperature in the expulsion stage and/or supplying supporting fuels in the combustion stage. In the case of oil-containing raw materials of low quality, such control is not possible, however, because of the risk of coking.